12

I need to call a specific command in an interval of about 5 sec. How would I setup a daemon/process running in the background or something similar to do that? I looked at cronjobs, but the minimum interval seems to be 1 minute. Any advice is appreciated ;)

Fedora is the system.

EDIT the command would be a bashscript, so "watch" wouldn´t do it I think.

10
(
  while true
  do
    your-command-here
    sleep 5
  done
) &
disown
| improve this answer | |
  • what is disown for? what if I run without it? – Hans Jan 19 '11 at 15:09
  • @Marcel, disown removes the last job from the shell job table, making it sort of a daemon, like you asked. It is not a real daemon because it is still attached to terminal and is in the same process group, but it will keep running after you close the shell. – Juliano Jan 19 '11 at 15:14
  • okay great, that would work :D Just for curiosity how would i "make" a daemon? – Hans Jan 19 '11 at 15:24
  • @Marcel the simple way is to call daemon(3) from C or other language with library access (not from a shell script). This is the hard way. – Juliano Jan 19 '11 at 15:35
14

Why do you think 'watch' will not work?

$ cat periodic.sh
#!/bin/bash
echo $(date)
$ chmod +x periodic.sh

$ watch -n 5 ./periodic.sh
| improve this answer | |
  • what if I log out? the script should continue running. – Hans Jan 19 '11 at 15:13
  • It will stop, but you can use nohup watch -n 5 ./periodic.sh > periodic.log & and store the output. – naufraghi Apr 28 '11 at 10:07
  • for piping use the '' quoting because th "command is given to "sh -c" which means that you may need to use extra quoting to get the desired effect" – andrej Mar 22 '13 at 10:00
2

Maybe with nohup? It's designed to let a job run after the shell is closed.

You can also use screens.

| improve this answer | |
1

The watch command is appropriate in your case, i would use a terminal multiplexer (e.g. tmux, screen, etc.) and then run the command using

watch -n 5 ./script.sh

In that case even if you close the terminal or ssh connection to the machine the script would still be running.

The only limitation of this approach is that the script will run every 5 seconds only if it has completed its execution within that time interval.

| improve this answer | |
  • Since the OP explicitly stated that in his opinion watch wouldn't do it, please explain why your answer overcomes this limitation or at which point you think the OP was mistaken about watch being unsuitable for the task. – AdminBee Nov 7 '19 at 10:11

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